(a) Field of the Invention
The invention relates generally to agrochemical compositions and specifically to compositions and methods for controlled pre-harvest defoliation of crop plants, such as for desiccation of potatoes and the like crop cultures.
(b) Description of the Prior Art
Defoliating agents or defoliants are used in agriculture to control undesirably strong development of crop plant foliage and in order to initiate at an early stage, or to accelerate, normal plant decay including defoliage and/or desiccation of leaves and stems of crop plants which decay is part of the normal vegetation cycle but would take longer without use of such defoliants or desiccants. This is of particular importance for controlled initiation or acceleration of decay and desiccation of crop plant components that preclude, or render difficult, the harvesting operation including use of harvesting machines.
The use of defoliants in Central Europe is of commercial importance mainly in connection with potato cultures. Potato harvest starts when the leaves and overground stem portions dry up or desiccate near the end of the vegetation period, and a delay of desiccation due to anomalies of weather conditions before or at the harvest period may be detrimental in that actual harvest may be complicated or even impossible after commencement of rainy or extremely cold fall period weather. Thus, controlled pre-harvest defoliation or desiccation of the potato plants is desirable so that termination of vegetation can be initiated and controlled essentially independent of climatic conditions.
Approved defoliants or desiccants (also called vine desiccants) used at present in substantial quantities are preparations containing, as active ingredient, 4,6-dinitro-o-kresol ("DNOC"), or 2-sec.-butyl-4,6-dinitro-phenol (common name "Dinoseb"), or 1,1'-ethylene-2,2'-bipyridyllium salts (common name "Diquat").
Obviously, both selection as well as admission for use by government authorities of such active ingredients does not only depend upon the actual chemical effectiveness of such substance per se but upon other important parameters, such as toxicity and other characteristics of the active substance under consideration including possible influences upon the environment, chemical decomposition characteristics, the tendency to form residues in the soil, consequences for subsequent crops or "carry-over" and--last but not least--consequences upon the quality of the harvested products.
The three substances mentioned above meet these selection criteria to an extent that is assumed to meet reasonable standards. This does not justify the assumption, however, that these substances or active ingredients are entirely free of problems. For example, those persons that have to handle or apply the agents or compositions find that these substances have rather inconvenient properties and are not entirely free of hazards; for example, both DNOC and Dinoseb cause a penetrating yellow coloration of the skin and Diquat, in concentrated form, can damage the finger nails and cause other irritations.
Accordingly, there is a need to provide for pre-harvest defoliants and methods with the same defoliant effectiveness as the best prior art compositions and methods but without the disadvantages just mentioned.